The last time the American side of the falls ran dry was over 46 years ago when a temperary dam was installed with plans to remove rocks that had collected at the base of the cliff.

Two rockslides from the plate of the falls caused a large amount of rock to be collected at the base first in 1931, and then again in 1954. Researchers believed if the errosion continued, it would lead to the end of the falls.

Almost 28,000 tons of rock, spanning 600 feet were put in place across the Rigara River, stopping the Ameican Falls on June 12th, 1969. Over 60,000 gallons of water was diverted to the Canadian side of the falls.

Engineers worked for six months to remove rocks and conduct geological testing. The temporary dam was exploded on November 25th, 1969 as over 2,600 onlookers watched the water return to the falls.

If the falls are stopped again, the project isn’t expected to see them run dry until 2019.

The bridge designs being considered come with a price tag between $25-million and $35-million US.

Ontario Power Generation, which helps control the flow of water over the falls along with its American counterparts, says it won’t result in more power for Canada because the turbines are upriver of the falls.